Systems for testing valves

ABSTRACT

A chamber assembly for testing a valve includes a proximal chamber portion that defines a proximal interior space, and a distal chamber portion that defines a distal interior space. The distal interior space includes a gas space. When a liquid is inserted into the proximal and distal chambers there is an interface between the liquid and a gas in the gas space. A valve holder is disposed adjacent to the proximal interior space and the distal interior space. The valve holder is configured to receive the valve in a bore of the valve holder. A shortest distance between a center of the valve when in the bore and the interface is at least about 45 mm.

This application is a continuation-in-part of U.S. patent applicationSer. No. 14/306,508 filed on Jun. 17, 2014 and titled as above.

BACKGROUND Technical Field

This document relates to systems and methods for testing valves. Forexample, this document relates to systems and methods for acceleratedlife testing of prosthetic heart valves.

Background Information

Accelerated life testing (also known as accelerated wear testing ordurability testing) is the process of testing an item by subjecting itto conditions (e.g., cycle time, stress, strain, temperatures, voltage,vibration, pressure, etc.) in excess of its normal service parameters inan effort to uncover faults and potential modes of failure in a reducedamount of time. Accelerated life testing can be been used to studymaterials, design concepts, design modifications, and durabilityvariations caused by changes in manufacturing techniques.

The ISO 5840-3:2013 standard outlines an approach for qualifying thedesign and manufacture of heart valve prostheses. ISO 5840-3:2013requires that mechanical heart valves be tested for at least 600 millioncycles (equivalent to 15 years in vivo), and that biological heart valveprostheses be tested for at least 200 million cycles (equivalent to 5years in vivo) in pulsatile flow simulators using a range of pressuresseen in physiologic conditions. The cyclic test must also meet thefollowing two requirements: 1) the test valve must open and closesufficiently each cycle, and 2) during at least 5% of each cycle, thedifferential pressure across the valve (transvalvular ΔP) must be atleast a specified pressure (e.g., 100 mmHg for aortic valves and 120mmHg for mitral valves).

SUMMARY

This document provides systems and methods for testing various kinds ofvalves. For example, this document provides systems and methods foraccelerated life testing of prosthetic heart valves. The systems andmethods provided herein are well-suited for use with a wide variety oftypes of prosthetic and biological heart valves. For example, prostheticheart valves that are intended for deployment at anatomical sitesincluding, but not limited to, aortic valves, mitral valves,atrioventricular valves, pulmonary valves, and the like, can be testedusing the systems and methods provided herein. Further, valve types suchas, but not limited to, mechanical valves, tissue (biological) valves,tissue-engineered valves, surgically implantable valves, transcatheterimplantable valves, and the like, can be subjected to accelerated lifetesting using the systems and methods provided herein. The systems andmethods provided herein can also be used for accelerated life testing ofnon-medically related valves.

All examples and features mentioned below can be combined in anytechnically possible way. In one aspect, a chamber assembly for testinga valve includes a proximal chamber portion that defines a proximalinterior space, and a distal chamber portion that defines a distalinterior space. The distal interior space includes a gas space. When aliquid is inserted into the proximal and distal chambers there is aninterface between the liquid and a gas in the gas space. A valve holderis disposed adjacent to the proximal interior space and the distalinterior space. The valve holder is configured to receive the valve in abore of the valve holder. A shortest distance between a center of thevalve when in the bore and the interface is at least about 45 mm.

Embodiments may include one or more of the following features, or anycombination thereof. The shortest distance between the center of thevalve when in the bore and the interface is at least about 50 mm. Theshortest distance between the center of the valve when in the bore andthe interface is at least about 55 mm. The shortest distance between thecenter of the valve when in the bore and the interface is at least about60 mm. The shortest distance between the center of the valve when in thebore and the interface is at least about 65 mm. An area of the interfaceA_(s) in cm with the liquid at rest is set so that an agitated liquiddepth D_(a) is no greater than a distance from the interface to a topedge of the valve. The agitated liquid depth is a distance that agitatedliquid with bubbles reaches below the interface in cm during testing ofa valve. The chamber assembly includes one or more baffles which arelocated in the distal interior space at least partially on a first sideof the interface and at least partially on a second side of theinterface with the liquid at rest. The one or more baffles reducesreflection of waves in the liquid off sides of the distal chamber.

In another aspect, a system for testing a valve includes a chamberassembly with a proximal chamber portion that defines a proximalinterior space, and a distal chamber portion that defines a distalinterior space. The distal interior space includes a gas space. When aliquid is inserted into the proximal and distal chambers there is aninterface between the liquid and a gas in the gas space. A valve holderis disposed adjacent to the proximal interior space and the distalinterior space. The valve holder is configured to receive the valve in abore of the valve holder. An area of the interface A_(s) in cm with theliquid at rest is set so that an agitated liquid depth D_(a) is nogreater than a distance from the interface to a top edge of the valve,wherein the agitated liquid depth is a distance that agitated liquidwith bubbles reaches below the interface in cm during testing of avalve.

Embodiments may include one of the above and/or below features, or anycombination thereof. The relationship between A_(s) and D_(a) issubstantially D_(a)=−mA_(s)+b with m being in the range of about −0.6 toabout −2.2 and b being in the range of about 13.1 to about 20.8. Therelationship between A_(s) and D_(a) is substantiallyD_(a)=−1.6A_(s)+18.4.

In another aspect, system for testing a valve includes a chamberassembly with a proximal chamber portion that defines a proximalinterior space, and a distal chamber portion that defines a distalinterior space. The distal interior space includes a gas space. When aliquid is inserted into the proximal and distal chambers there is aninterface between the liquid and a gas in the gas space. One or morebaffles are located in the distal interior space at least partially on afirst side of the interface and at least partially on a second side ofthe interface with the liquid at rest. The one or more baffles reducereflection of waves in the liquid off sides of the distal chamberportion. A valve holder is disposed between the proximal interior spaceand the distal interior space. The valve holder is configured to receivethe valve in a bore of the valve holder.

Embodiments may include one of the above features, or any combinationthereof.

Particular embodiments of the subject matter described in this documentcan be implemented to realize one or more of the following advantages.First, in some embodiments the accelerated life testing systems providedherein are capable of operating at a high rate of speed. For example, insome embodiments the systems can operate at about 30 Hz or above. Assuch, the duration of the accelerated life tests can be shortened incomparison to systems that operate at slower speeds. Second, in someembodiments the test requirement for the transvalvular ΔP to be at leasta specified pressure during at least 5% of the cycle can be met withminimal ΔP overshoot. This feature can minimize valve overstress duringthe test process. Such overstress can cause overly harsh test conditionsand may lead to unrepresentative test results. Third, the pulsatile flowsystems for accelerated life testing provided herein are configured forconvenience of use. For example, in some embodiments portions of thetest equipment can be removed from the pulsatile flow system andinstalled on other test equipment in a user-friendly manner. Fourth, thesystems provided herein are configured to allow visual observation andanalysis of the valves during the test process. Such visual analysis canbe performed using normal eyesight, or using cameras such as, but notlimited to, automated machine vision systems in some embodiments. Fifth,in some embodiments the systems provided herein are configured tosubstantially replicate physiological conditions and/or meet ISO testrequirements while using a standard sine wave input waveform. However,in some embodiments non-sinusoidal waveforms may be used. Sixth, someaspects of the system (e.g., the test chamber) are designed to beadjustable to provide the fluid dynamic performance to meet the user'stest requirements. That is, in some embodiments the fluid dynamicperformance of the system can be tuned to achieve the performancedesired by adjusting, for example, the return orifice size or air cavitysize. What is more, in some embodiments closed loop controls forautomatic system tuning during the test process are included.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention pertains. Although methods and materialssimilar or equivalent to those described herein can be used to practicethe invention, suitable methods and materials are described herein. Allpublications, patent applications, patents, and other referencesmentioned herein are incorporated by reference in their entirety. Incase of conflict, the present specification, including definitions, willcontrol. In addition, the materials, methods, and examples areillustrative only and not intended to be limiting.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description herein. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is perspective view of an example accelerated life testing systemin accordance with some embodiments.

FIG. 2A is a side view of the accelerated life testing system of FIG. 1.

FIG. 2B is a front view of the accelerated life testing system of FIG.1.

FIG. 3 is an exploded side view of the accelerated life testing systemof FIG.

FIG. 4A is a front view of an example test chamber for an acceleratedlife testing system in accordance with some embodiments.

FIG. 4B is cross-sectional side view of the test chamber of FIG. 4A.

FIG. 5 is an exploded view of the test chamber of FIG. 4B.

FIG. 6A is an exploded side view of an example valve holder andprosthetic valve sub-assembly.

FIG. 6B is a front view of the valve holder and prosthetic valvesub-assembly of FIG. 6A.

FIG. 7 is a side view of the test chamber of FIG. 4B that is depictedpartially filled with a liquid and undergoing visual inspection.

FIG. 8 is a block diagram of the accelerated life testing system of FIG.1.

FIG. 9A is an example input waveform that can be used for theaccelerated life testing systems in accordance with some embodiments.

FIG. 9B are example waveforms of test chamber pressures and the testchamber differential pressure in accordance with some embodiments.

FIG. 10 is an isometric view of an example portable portion of a testchamber including the valve holder.

FIG. 11 is a side view of another example embodiment of a test chamberfor an accelerated life testing system in accordance with someembodiments.

FIG. 12 is a side view of another example embodiment of a test chamberfor an accelerated life testing system in accordance with someembodiments.

FIG. 13 is a side view of another example embodiment of a test chamberfor an accelerated life testing system in accordance with someembodiments.

FIG. 14 is a side view of another example embodiment of a test chamberfor an accelerated life testing system in accordance with someembodiments.

FIG. 15 is a perspective view of a baffle that is usable in the exampleshown in FIG. 14. Like reference numbers represent corresponding partsthroughout.

DETAILED DESCRIPTION

This document provides systems and methods for testing various kinds ofvalves. For example, this document provides systems and methods foraccelerated life testing of prosthetic heart valves.

Referring to FIGS. 1, 2A, and 2B an example multi-station acceleratedlife testing (ALT) system 100 includes multiple chambers 110, aframework 120, and multiple bellows 130. The chambers 110 and thebellows 130 are mounted to and are supported by the framework 120. Eachindividual chamber 110 is in fluid communication with a correspondingindividual bellows 130 located below the individual chamber 110, or aflexible membrane diaphragm 121 can be optionally used between thechamber 110 and bellows 130 in some embodiments. The bellows 130 can beaxially extended or compressed, as will be described further below.

The internal spaces of the chamber 110 and the bellows 130 can receive aliquid (e.g., saline, water, and the like). Accordingly, an axialextension or compression of the bellows 130 will initiate acorresponding movement of the liquid within the bellows 130 and withinthe chamber 110. In regard to embodiments that include the optionalflexible membrane diaphragm 121, such movements of the bellows 130create pressure changes in the liquid contained in the bellows 130 thatare communicated to the liquid in the chamber 110 via the flexiblemembrane diaphragm 121. As will be described further below, a valve(e.g., a prosthetic heart valve) can be mounted within the chamber 110.An axial actuation of the bellows 130 can therefore move a liquidthrough the valve such that the valve is cycled between an opened stateand a closed state.

In the example ALT system 100, six stations that each include anindividual chamber 110 and a corresponding individual bellows 130 areincluded. In other system embodiments, fewer or more than six stationscan be included. For example, in one alternative embodiment an ALTsystem can include a single chamber 110 and a single correspondingbellows 130. In general, the ALT system 100 is scalable such that anypractical number of test stations can be included.

Referring to FIG. 3, the ALT system 100 (shown in an exploded side view)can also include a linear actuator 140. The bottom end of the linearactuator 140 can be mounted to the framework 120, and the active end ofthe linear actuator 140 can be attached to the bellows 130. In someembodiments, an individual linear actuator 140 can be configured todrive two or more bellows 130.

In some embodiments, the linear actuator 140 is an electromagneticactuator that includes one or more stator coils and flexural suspensionelements that are connected to each end of an armature of the actuator140. The flexural suspension elements allow frictionless movement of thearmature in a vertical direction of travel while providing resistance tomovement of the armature in other degrees of freedom (e.g., translation,rotation). During operation of the electromagnetic actuator 140,magnetic fields from a magnetic assembly that has one or more permanentmagnets interact with the magnetic fields generated by the electricalcurrent flowing in the stator wire coils. This interaction causes thearmature to move linearly up and down relative to the housing framework120. In some embodiments, a displacement sensor 141 (e.g., an LVDT, andthe like) is optionally included to detect and acquire data regardingthe linear movement of the actuator 140. The data output from thedisplacement sensor 141 can be used, for example, for closed-loopcontrol of the actuator 140 in some embodiments. In some embodiments,the displacement sensor 141 can be used, for example, as an indicatorfor piston movement or to indicate fluid transfer per cycle with anestablished actuator to fluid volume relationship.

The linear movement of the actuator 140 induces, in turn, axialextension and compression of the bellows 130. A liquid inside of thebellows 130 will be withdrawn from or propelled into the chamber 110 towhich the bellows 130 is attached. This movement of liquid can cause anopening and closing of a valve that is located within the chamber 110.In some embodiments, other types of fluid displacement members can besubstituted for the bellows 130 (e.g., a sliding piston or a rollingdiaphragm, and the like). In some embodiments, other types of actuatordevices can be substituted for the linear electromagnetic actuator 140(e.g., a rotary motor with a crank mechanism, and the like). Variouscombinations and sub-combinations of fluid displacement members andactuator devices are envisioned within the scope of this disclosure.

Referring to FIGS. 4A, 4B, and 5, the chamber 110 includes a distalchamber 111, a valve holder 114, and a proximal chamber 118. When thechamber 110 is assembled, the valve holder 114 is disposed between thedistal chamber 111 and the proximal chamber 118. An end portion 119 ofthe proximal chamber 118 can be coupled to a bellows (e.g., the bellows130 of the ALT system 100). In such a case, an extension or compressionof the bellows can withdraw or propel a volume of liquid in relation tothe chamber 110 such that the volume of liquid is transferred betweenthe proximal and distal chambers 111 and 118. In that case, the volumeof liquid passes through the valve holder 114. To facilitate the passageof liquid, the distal chamber 111 includes a compliancy feature (e.g.,airspace 182 as described below in reference to FIG. 7, or another typeof compliancy feature such as, but not limited to, a flexible member).

In some embodiments, the components of the chamber 110 are made ofpolymeric materials. For example, in some embodiments the components ofthe chamber 110 are made of polymeric materials such as, but not limitedto, polycarbonate (e.g., LEXAN), polyoxymethylene (e.g., DELRIN),acrylic, acetyl, PVC, and the like. Such materials can be formed intothe required shapes by machining, molding, 3D printing, and/or by anyother suitable processes and combinations of processes. In someembodiments, transparent or near transparent materials are used forcomponents of the chamber 110 (e.g., at least the proximal and distalchambers 111 and 118). As such, the interior of the chamber 110 can beadvantageously visible in some embodiments. In some embodiments, threeor more sides of the chamber 110 assembly are substantially transparent.

The distal chamber 111 is releasably coupled to the proximal chamber118. In some embodiments, one or more latches, clamps, pins, hinges,threaded connections, bayonet connections, circumferential clamps,and/or other types of quick release joining mechanisms are used toreleasably couple the distal chamber 111 to the proximal chamber 118 ina convenient manner. Such user-friendly mechanisms for assembling anddisassembling the chamber 110 can be desirable because at certain timesduring valve durability testing the chamber 110 may need to bedisassembled so that other types of tests or inspections can beperformed on the valves.

In the depicted embodiment, a lens 112 is attached to the distal chamber111. The lens 112 can be a transparent member such as polycarbonate,tempered glass, and the like. The lens 112 can provide a direct view ofa valve located within the valve holder 114. While in the depictedembodiment, the lens 112 is a separate component that is attached to thedistal chamber 111, in other embodiments the lens 112 can be integrallyformed in the wall of the distal chamber 111.

To make the chamber 110 a liquid tight enclosure, seals can be includedat the interface between various components of the chamber 110. Forexample, a seal 117 is located at the interface between the distalchamber 111 and the proximal chamber 118. Also, a seal 113 is located atthe interface between the distal chamber 111 and the lens 112. One ormore seals 116 a and 116 b can also be located around the periphery ofthe valve holder 114. The seals 116 a and 116 b can inhibit paravalvularleaks between the distal chamber 111 and the proximal chamber 118. Insome embodiments, one or more seals can also be located at the interfacebetween the end portion 119 of the proximal chamber 118 and the bellows.The seals can be constructed as O-rings, D-rings, washers, gaskets, andthe like, and can be made of materials such as, but not limited to,ethylene propylene diene monomer (EPDM), Nitrile, silicone,fluorocarbons, polyurethane, neoprene, fluorinated ethylene propylene(FEP), and the like.

One or more ports 111 p can be included in the distal chamber 111.Similarly, one or more ports 118 p can be included in the proximalchamber 118. Such ports 111 p and 118 p can be used to access theinterior open spaces that are defined by the chambers 111 and 118respectively. The ports 111 p and 118 p can be used for various purposessuch as, but not limited to, draining liquid from within the chambers111 and 118, mounting one or more sensors within the chambers 111 and118, attaching a compliance chamber to the proximal chamber 118 and/orthe distal chamber 111, and mounting one or more lights for illuminatingthe interior of the chambers 111 and 118. For example, in some cases theports 111 p and 118 p can be used to mount pressure sensors that areused for monitoring the pressure of the liquid within the chambers 111and 118. In addition, in some cases the ports 111 p and 118 p can beused to mount lights (e.g., LEDs) that can be used to enhance theviewing of a valve that is undergoing testing. For example, as will bedescribed further below, in some embodiments such lights can be used astiming lights so that the high-speed operation of the valve undergoingtesting can be observed as if it were operating at a slower speed.

The proximal chamber 118 includes an inlet passageway 118 i. The inletpassageway 118 i conveys liquid between the bellows and the chambers 111and 118. In some embodiments, the inlet passageway 118 i is configuredto convey a jet of liquid from the bellows to the proximal chamber 118that flows substantially coaxial to the central axis of the valve holder114. In the depicted embodiment, to achieve the substantially coaxialflow the inlet passageway 118 i is radiused and positioned such that theouter radius of the inlet passageway 118 i is approximately aligned withthe axis of the central axis of the valve holder 114. In someembodiments, other configurations of the inlet passageway 118 i inrelation to the valve holder 114 can be used.

The valve holder 114 includes a central bore 114 b that is lined with aremovable sleeve 115. The inner diameter of the sleeve 115 is configuredto receive a valve body therein. The interface between the innerdiameter of the sleeve 115 and the outer diameter of the valve body isintended to be substantially liquid-tight to avoid paravalvular leaksduring testing. Thus, the sleeve 115 can be made of a compliantmaterial. For example, in some embodiments the sleeve 115 can be made ofmaterials such as, but not limited to, silicone, neoprene, and othersuitable elastomers. In some embodiments, the inner diameter of thesleeve 115 may include a circumferential groove or other such surfacefeatures to facilitate mounting the valve to be tested therein. Inparticular embodiments, the inner diameter of the sleeve 115 may bedesigned to simulate the geometry (physiology) of a valve implant site.In some embodiments, the sleeve 115 is compliant such that if the valveΔP reaches an over-peak condition, the compliance may reduce the effectsof the condition. That is, in some embodiments the sleeve 115 isconfigured to deflect in response to a high ΔP between the proximalinterior space and the distal interior space of the chamber 110.

Referring to FIGS. 6A and 6B, the valve holder 114 can receive anexample prosthetic heart valve 150 within the central bore 114 b of thevalve holder 114. The valve 150 is a one-way valve. That is, liquidflowing in one direction in relation to the valve 150 will open thevalve 150 so that the liquid can flow therethrough (e.g., referring toFIGS. 4A and 4B, as liquid flows from the proximal chamber 118 towardsthe distal chamber 111 the valve 150 will open). However, when theliquid starts to flow in the opposite direction in relation to the valve150, the valve 150 will close such that the liquid will be preventedfrom flowing therethrough. Alternatively, in some embodiments the valve150 is mounted in the opposite direction such that the valve 150 willclose when liquid is transferred from the proximal chamber 118 to thedistal chamber 111, and the valve 150 will be forced open when liquid istransferred from the distal chamber 111 to the proximal chamber 118.

To facilitate liquid flow through the valve holder 114 in the directionwhich causes the valve 150 to be closed, the valve holder 114 includesone or more return flow orifices 114 ou and 114 ol. In the depictedembodiment, the return flow orifice 114 ou is an upper orifice, and thereturn flow orifice 114 ol is a lower orifice. Having an upper orifice114 ou and a lower orifice 114 ol can be advantageous in someembodiments. For example, the upper orifice 114 ou can facilitateairflow therethrough in the event that some air (e.g., bubbles) becomesentrapped in the proximal chamber 118 (as will be explained furtherbelow, some entrapped air can be better accommodated in the distalchamber 111). Further, the lower orifice 114 ol can facilitate fluidflow therethrough to assist with gravitational drainage of the liquidfrom the chambers 118 and 111. Accordingly, in some embodiments one ormore return flow orifices are positioned on the valve holder 114 suchthat at least a first return flow orifice of the one or more return floworifices 114 ou and 114 ol is located in an upper portion of the chamber111 and 118, and at least a second return flow orifice of the one ormore return flow orifices 114 ou and 114 ol is located in a lowerportion of the chamber 111 and 118.

While the depicted embodiment includes two return flow orifices 114 ouand 114 ol, in some embodiments a single orifice or more than twoorifices are included. For example, in some embodiments the valve holder114 can include three, four, five, six, seven, eight, nine, ten, or morethan ten orifices.

In the depicted embodiment, an interchangeable valve holder end plate114 p is included. In some embodiments, one purpose of the valve holderend plate 114 p can be to configure the valve holder 114 to have adesired number of return flow orifices. In addition, in some embodimentsanother purpose of the valve holder end plate 114 p can be to configurethe sizes of the one or more return flow orifices. While in the depictedembodiment the return flow orifices 114 ou and 114 ol are located in thevalve holder 114, it should be understood that, additionally oralternatively, in some embodiments return flow orifices can be locatedin other structures of the chamber 110. For example, in some embodimentsthe return flow pathway can be connected between the ports 118 p and 111p.

It should be understood that, as will be described further below, thequantity and size of the one or more return flow orifices (e.g.,orifices 114 ou and 114 ol) influences the pressure differential betweenthe proximal and distal chambers 118 and 111 (refer to FIGS. 4A and 4B).This pressure differential is also the pressure that the valve 150 isexposed to when the valve 150 is closed.

Briefly, the effect that the quantity and size of the one or more returnflow orifices have on the differential pressure is explained as follows.An amount of liquid will be transferred through the open valve 150 asthe bellows 130 compresses (e.g., refer to FIGS. 1-3). In general, theALT system will be configured such that the amount of liquid to betransferred will be that amount that is needed to sufficiently open thevalve. That same amount will need to be returned through the return floworifices, and within a particular period of time (the time during whichthe bellows 130 is extending). Therefore, a small total area of returnorifice will result in a higher differential pressure, while a largetotal area of return orifice size will result in a lower differentialpressure. In this fashion, selection of the quantity and/or size of thereturn flow orifices can influence the pressure that the valve 150 isexposed to when the valve 150 is closed. In some implementations, anopen area of the one or more return flow orifices is selected based on asize of a valve 150 to be tested.

In some embodiments, the total area of return flow orifices isadjustable without disassembling the chamber 110 (refer to FIGS. 4A and4B). For example, in some embodiments one or more of the return floworifices can be configured as a valve-like device (e.g., a gate valve,ball valve, needle valve, etc.) that can be adjusted externally to thechamber 110. In some embodiments, the adjustment can be performedmanually, including while the test system is operating. In particularembodiments, the adjustment can be performed automatically. In some suchembodiments, a valve actuator and controls can be included such thatautomated adjustments of the total area of return flow orifices can bemade to control towards a target operating parameter such as, but notlimited to, the differential pressure characteristic across the valve150 when the valve 150 is closed (e.g., the peak differential pressureacross the valve 150 when the valve 150 is closed).

Referring to FIG. 7, in some embodiments the chamber 110 can be filledwith a liquid 180 and an airspace 182. The airspace 182 is located inthe distal chamber 111 and is in direct contact with the liquid 180. Theliquid 180 can be liquids such as, but not limited to, water, saline,culture media, and the like. The airspace 182 can be filled with a gassuch as air, CO2, and the like. While the volume of liquid 180 isessentially incompressible, the volume of the airspace 182 iscompressible.

During operation of the chamber 110, the airspace 182 is cyclicallycompressed and decompressed in synch with the cyclical motion of thebellows 130 (refer to FIGS. 4A and 4B). That cyclic compression anddecompression of the airspace 182 occurs as follows. As the bellows 130compresses, some of the liquid 180 from the bellows 130 is expelled intothe proximal chamber 118. The liquid 180 that is expelled into theproximal chamber 118, in turn, causes a same amount of liquid 180 toflow through the valve 150 and return flow orifices into the distalchamber 111. That flow of liquid 180 causes the valve 150 to open. Dueto the amount of liquid 180 that flowed into the distal chamber 111, thevolume of the airspace 182 decreases equivalently. The aforementionedactions continue until the bellows 130 ends its compression phase.

After the compression phase of the bellows 130, the bellows 130 beginsto extend. As the bellows 130 extends, some amount of liquid 180 isdrawn out of the chamber 110. In total, the same amount of liquid 180that was expelled from the bellows 130 during its compression phase willbe drawn out of the chamber 110 and return back into the bellows 130during the bellow's 130 extension phase. That removal of the liquid 180from the chamber 110 will result in an equivalent increase in the volumeof the airspace 182.

From the foregoing description regarding the liquid 180 and the airspace182, it should be understood that in some embodiments the airspace 182functions like a gas spring. That is, the airspace 182 is compressedduring a portion of the test cycle and expanded during another portionof the test cycle.

It can also be understood that the nominal volume of the airspace 182will affect the force required from the bellows 130 to drive the liquid180 during the compression phase of the bellows 130. For example, lesswork will be required by the bellows 130 to compress the airspace 182 ifthe airspace 182 is larger than if the airspace 182 is smaller. That istrue because, in accordance with the ideal gas law, compressing a largeairspace 182 by a volumetric amount will result in a smaller pressureincrease of the airspace 182 than will compressing a small airspace 182by the same volumetric amount. The compressed airspace 182 can alsofacilitate flow of the liquid 180 from the distal chamber 111 to theproximal chamber 118 via the return flow orifices 114 ou and 114 ol(refer to FIG. 6B) during the extension of the bellows 130. A negativepressure gradient across the valve 150 during and after closing of thevalve 150 is desired for the functional test of the valve 150. Thepositive pressure within the airspace 182 and the negative pressurecreated by the extension of the bellows 130 facilitate that negativepressure across the valve 150. In some circumstances, this can serve toreduce the amount of vacuum pulled by the bellows 130 during testing.

Using the aforementioned principles regarding the airspace 182, thevolume of the airspace 182 can be selected (as one factor) to provide adesired pressure operation range of the test system 100. For example,the maximum pressure that the liquid 180 will attain (at the end of thecompression of the bellows 130) is affected by the nominal size of theairspace 182. The change in volume of the airspace 182 throughout thecompressional stroke of the bellows 130, relative to the nominal size ofthe airspace 182 at least partly defines the maximum pressure (e.g., a 1ml volume change of a 2 ml airspace 182 will produce greater pressuresthan a 2 ml volume change of a 20 ml airspace 182). In someimplementations, the airspace 182 is sized such that the maximumpressure of the liquid 180 is relatively similar to the maximum pressurethat the valve being tested will be exposed to in expected usagescenarios. For example, the maximum pressure that an aortic heart valvewill be exposed to is the systolic pressure (e.g., nominally about 120mmHg to about 160 mmHg). Therefore, in one example the volumetric sizeof the airspace 182 may be selected so that the maximum pressure of theliquid 180 is about 150 mmHg during the systolic phase. In otherexamples, other pressure levels can be designed for by selecting asuitable volumetric size of the airspace 182.

In some embodiments, one or more heating elements (not shown) and one ormore temperature sensors (not shown) are included to provide the abilityto control and measurement of the liquid 180. Such heating elements andtemperature sensors can be located in various locations such as, but notlimited to, near the interface between the end portion 119 of theproximal chamber 118 and the bellows. The heating elements andtemperature sensors may also be positioned in other locations such thatthe temperature of the liquid 180 can be measured and/or controlled asdesired.

Still referring to FIG. 7, in the depicted embodiment a longitudinalaxis 155 of the chamber 110 is tilted at an angle of about 35° fromhorizontal. In other embodiments, angles of about 0° to about 20°, orabout 15° to about 35°, or about 30° to about 50°, or about 45° to about65°, or about 60° to about 80°, or about 75° to about 90° can be used.

In some embodiments, the tilt of the longitudinal axis 155 provides somebenefits. For example, if any air becomes inadvertently entrained withinthe liquid 180, the air will tend to ascend towards the airspace 182since the airspace 182 is at the highest elevation within the chamber110. The inadvertently entrained air will tend to have a less negativeimpact on the testing if the inadvertently entrained air resides withinthe airspace 182 rather than in other places within the chamber 110. Inanother example, the tilt of the longitudinal axis 155 can allow forobservation of both the top and the bottom of the valve 150. That is, asrepresented by an eye symbol 170, an observation of the bottom of thevalve 150 can be made through the end wall of the proximal chamber 118.Further, the ergonomics associated with viewing of the valve 150 isbenefitted by the tilt of the longitudinal axis 155. In addition, asrepresented by a camera 160, an observation of the top of the valve 150can be made through the end wall of the distal chamber 118.

The camera 160 can be used to view the operation of the valve 150 duringthe testing. The camera 160 can be a still frame camera or a videocamera. In some embodiments the camera 160 is a high-speed video camera.As described previously, in some embodiments one or more lights forilluminating the interior of the chambers 111 and 118, and the valve 150are included. For example, in some embodiments such lights can be usedas timing lights so that the high-speed operation of the valve 150 canbe observed by the camera 160 as if it were operating at a slower speed.

In some embodiments, the camera 160 can be part of a machine visionsystem. In some such embodiments, the camera 160 and machine visionsystem can be used to determine the extent to which the valve 150 opensduring testing (e.g., a number of pixels corresponding to an open areaof the valve 150 can be quantified). The openness (also referred toherein as the effective open area) of the valve 150 may be a parameterthat needs to be verified during the performance of some durabilitytesting protocols. Further, by connecting the camera 160 and machinevision system to a control system of the test system 100, closed-loopcontrol using the machine vision system can be performed in someembodiments. For example, the test system 100 control system canautomatically adjust the operation of the test system 100 to attain athreshold level of open area of valve 150 in some embodiments.Furthermore, it should be understood that such a machine vision systemcan be used to detect valve failure through user interaction orautomatically through a closed-loop control.

Referring to FIG. 8, a control system 200 for the ALT systems providedherein can include a computerized controller 210, a signal conditioner220, a power supply 230 (which can include an amplifier stage in someembodiments), and an actuator and chamber assembly 240. The componentsof the control system 200 are in electrical communication with eachother. That is, the component of the control system 200 can providevarious outputs and receive various inputs from each other so that theoverall control system 200 functions as desired. The components shownhere, their connections and relationships, and their functions, aremeant to be exemplary only, and are not meant to limit implementationsof the inventions described and/or claimed in this document.

The control system 200 includes the computerized controller 210. Thecomputerized controller 210 can be various forms of a digital computer,such as a laptop, desktop, workstation, PLC, server, mainframe,micro-controller, and other appropriate computers and combinations ofcomputers or computer parts. The computerized controller 210 can includeone or more processors, various formats of memory (volatile,non-volatile, hard disc, etc.), a GUI, various interface andcommunication devices and ports, and so on. Such devices may beinterconnected using various busses, and may be mounted on a commonmotherboard or in other manners as appropriate. The one or moreprocessors can process instructions for execution within thecomputerized controller 210, including executable instructions stored inthe memory.

The one or more processors of the computerized controller 210 maycommunicate with a user through a control interface and a displayinterface coupled to the display device. The display device may be, forexample, a TFT (Thin-Film-Transistor Liquid Crystal Display) display oran OLED (Organic Light Emitting Diode) display, or other appropriatedisplay technology. The display interface may comprise appropriatecircuitry for driving the display to present graphical and otherinformation to a user. Other kinds of devices can be used to provide forinteraction with a user as well; for example, feedback provided to theuser can be any form of sensory feedback (e.g., visual feedback,auditory feedback, or tactile feedback); and input from the user can bereceived in any form, including acoustic, speech, or tactile input. Thecontrol interface may receive commands from a user and convert them forsubmission to the one or more processors. In addition, an externalinterface may provide communication with the one or more processors, toenable near area communication of the computerized controller 210 withother devices. The external interface may provide, for example, forwired communication in some implementations, or for wirelesscommunication in other implementations, and multiple interfaces may alsobe used.

The control system 200 also includes the signal conditioner 220. Thesignal conditioner 220 can be configured to receive signals from varioussensors, (e.g., pressure or temperature sensors) and to manipulate thesignals for reception by the computerized controller 210. For example,in some embodiments the signal conditioner 220 may convert analog signalinputs to digital signals to be received by the computerized controller210. In addition, the signal conditioner 220 may perform other signalconversion activities such as amplification, filtering, isolation, andthe like. Further, in some embodiments the signal conditioner 220 mayreceive inputs from the computerized controller 210, which are thenconverted for receipt for another device such as the power supply 230(which can include a power amplifier in some embodiments).

The control system 200 also includes the power supply 230. The powersupply 230 provides electrical power to the actuator and chamberassembly 240 to drive the actuator (e.g., the electromagnetic actuator140 of FIG. 3). For example, the power supply 230 can receive an inputsignal from the signal conditioner 220, and the power supply 230 can, inturn, amplify the signal and send it to the actuator and chamberassembly 240. In some embodiments, the signal can be a waveform (e.g., asine wave or another shape). The power supply 230 can also provideelectrical power for a liquid heater located in the actuator and chamberassembly 240 in some embodiments.

The control system 200 also includes the actuator and chamber assembly240. In some embodiments, the actuator and chamber assembly 240 can beexemplified as the system 100 as described above (refer to FIGS. 1-3),for example. The actuator and chamber assembly 240 can receive theaforementioned inputs from the power supply 230, and can provide one ormore outputs to the signal conditioner 220. For example, such outputscan include, but are not limited to, one or more of the following(referring to FIGS. 1-7): a pressure of the proximal chamber 118, apressure of the distal chamber 111, a temperature of the liquid 180, adisplacement of the electromagnetic actuator 140, an output from thecamera 160 and machine vision system that indicates an openness of thevalve 150, and the like. Such output signals can be received by thesignal conditioner 220, converted as necessary, and passed on to thecomputerized controller 210. The computerized controller 210 can use theoutput signals as parameters in the control algorithms being run by thecontroller 210. The control algorithms can, in turn, generate updatedcontrol signals that can be output to the signal conditioner 220 asdescribed above. In this manner, the control system 200 can operate anALT system in a controlled fashion as desired. In some embodiments, eachtesting chamber has its own micro-controller for monitoring andcontrolling testing parameters (as slave systems) that are connected toa master system (e.g., a laptop computer, etc.), that at leastperiodically monitors the micro-controllers.

Referring to FIG. 9A, a graph 220 of actuator displacement versus timecan illustrate an example input waveform 222 that can be used for system100. The example waveform 222 is essentially a sine wave. However, insome embodiments other shapes of input waveforms 222 can be used.Further, the cyclic rate shown is just an example, faster and slowercyclic rates are envisioned within the scope of this disclosure.Additionally, it should be understood that the magnitude of the wavesignal, peak and valley values, and mean value are flexible and can beadjusted to achieve the desired pressure and volume flow profile fortesting.

The input waveform 222 is indicative of the movement of theelectromagnetic actuator 140, the bellows 130, and the flow of theliquid 180 (referring to FIGS. 1-7). Referring now to FIGS. 9A and 9B,it can be seen that the input waveform 222 causes correspondingfluctuations in a distal pressure curve 242, a proximal pressure curve244, and a differential pressure curve 246. The distal pressure curve242 represents the pressure of the liquid 180 in the distal chamber 111.The proximal pressure curve 244 represents the pressure of the liquid180 in the proximal chamber 118. The differential pressure curve 246represents the differences between the pressures 242 and 244 of thedistal chamber 111 and the proximal chamber 118.

The fluctuations of the pressure curves 242 and 244 can be described,briefly, as follows (also referring to FIGS. 1-7). The pressure curves242 and 244 rise as the bellows 130 axially contracts. The axialcompression of the bellows 130 forces some amount of the liquid 180 toexpel from the bellows 130 into the chamber 110. The flow of the liquid180 in the direction from the proximal chamber 118 to the distal chamber111 causes the valve 150 to open. Because the valve 150 is a relativelylarge opening, the pressure curves 242 and 244 rise substantiallyfollowing the same curve, and the differential pressure curve 246 isnear zero. As the bellows 130 reverses and begins to axially extend,some amount of liquid 180 begins to be drawn back into the bellows 130from the chamber 110. After the valve 150 closes, the liquid 180 mustflow through the one or more return flow orifices 114 ou and 114 ol. Theone or more return flow orifices 114 ou and 114 ol, being relativelysmall, cause a significant pressure drop in the proximal chamber 118 asthe liquid 180 flows through the one or more return flow orifices 114 ouand 114 ol. Therefore, the proximal pressure curve 244 (proximal chamber118) drops below the distal pressure curve 242 (distal chamber 111), andthe differential pressure curve 246 rises correspondingly. Thedifferential pressure curve 246 is the pressure across the valve 150 asa function of time.

From the foregoing description, it can be understood that the pressureacross the valve 150 is affected by the pressure drop of the liquid 180as it flows through the one or more return flow orifices 114 ou and 114ol. Additionally, as described above, the pressure drop of the liquid180 as it flows through the one or more return flow orifices 114 ou and114 ol is affected by the size and quantity of the one or more returnflow orifices 114 ou and 114 ol. Therefore, it holds that the pressureacross the valve 150 is affected by the size and quantity of the one ormore return flow orifices 114 ou and 114 ol. In some implementations ofsystem 100, it is desirable to substantially replicate the physiologicalconditions in which the valve 150 will be used. Therefore, for theprosthetic heart valve 150, the size and quantity of the one or morereturn flow orifices 114 ou and 114 ol can be selected to create adifferential pressure curve 246 substantially as shown (the pressureacross the valve 150 is essentially 0 mm Hg when the valve 150 is open,and at least 100 mmHg for part of the time when the valve 150 isclosed).

As stated in the Background, 5840-3:2013 requires that, during at least5% of each cycle, the differential pressure across the valve must be atleast a specified pressure (e.g., 100 mmHg for an aortic valve). Theenlarged portion of FIG. 9B shows an example of how the differentialpressure curve 246 relates to that requirement. In other words, during atime period ti, the differential pressure curve 246 is at or above 100mmHg (using the specified pressure for an aortic valve as an example),where time period ti is at least 5% of each cycle time T. In some casesduring ti, the differential pressure curve 246 may exceed 100 mmHg, upto a maximum differential pressure p₁. In general, it can be desirableto have a differential pressure curve 246 with a p₁ that is notsubstantially greater than 100 mmHg. That is the case because when p₁ issubstantially greater than 100 mmHg, the valve 150 is being stressedmore than what is required by ISO 5840:2005 (or as required by otherapplicable standards or relevant test conditions).

In some embodiments, the system 100 can be tuned to produce adifferential pressure curve 246 that (i) meets the requirement that,during at least 5% of each cycle, the differential pressure across thevalve must be at least a specified pressure (e.g., 100 mmHg for anaortic valve) and that (ii) has a p₁ that is not substantially greaterthan the specified pressure. Such tuning can be performed by selectingan appropriate combination of factors such as, but not limited to: thesize and quantity of the one or more return flow orifices 114 ou and 114ol, the cycle speed, the shape of the input waveform 222, the shape ofthe chamber 110, the volume of liquid 180 that is displaced during thecycle, the size and pressure of the airspace 182, and by locating theone or more return flow orifices 114 ou and 114 ol between the distalchamber 118 and the proximal chamber 111 such that there is a shortreturn flow path therebetween.

Referring to FIG. 10, a portable test chamber assembly 300 can includethe distal chamber 111, the valve holder 114, and a chamber cap 250. Theportable test chamber assembly 300 can provide a convenient way totransport a valve and test chamber arrangement between various teststands (e.g., between durability testing and pulse duplication testingapparatuses, for example). Further, the portable test chamber assembly300 can allow a user to assemble a valve with the valve holder 114 andwith a distal chamber 111, and then to store the assembly by attachingthe chamber cap 250. In some cases, a liquid can be added such that thevalve can be immersed in the liquid during transport or storage. Byusing the portable test chamber assembly 300, more efficient set up andmanagement of the overall testing process can be obtained. In someembodiments, the chamber assembly 300 can be used for static incubationof a valve that is cell-seeded until the cells/structure is at a statewhere the tissue can withstand some mechanical loading. In someembodiments, the chamber assembly 300 can be used to allow simulation ofsurgical implantation of transcatheter valves or similar, for example.

Referring to FIG. 11, an example cylindrical test chamber 400 embodimentcan include a base 402, a proximal chamber 410, a distal chamber 420, avalve holder 430, and an airspace 440. The cylindrical test chamber 400is configured to be useable with the other relevant components of thesystem 100, such as the framework 120, the bellows 130, and the actuator140 (refer to FIG. 3). The cylindrical test chamber 400 has acylindrical chamber shape (whereas the chamber 110 has a threedimensional rectangular shape). While in the depicted embodiment thecylindrical test chamber 400 is vertically arranged, in some embodimentsthe cylindrical test chamber 400 can be tilted as described above inregard to the chamber 110. The cylindrical test chamber 400 can alsoinclude one or more of the other features described above in regard tothe chamber 110.

Referring to FIG. 12, an example hexagonal test chamber 500 embodimentcan include a base 502, a proximal chamber 510, a distal chamber 520,and a valve holder 530 (an airspace can be included in the distalchamber 520 when the hexagonal test chamber 500 contains a liquid). Thehexagonal test chamber 500 is configured to be useable with the otherrelevant components of the system 100, such as the framework 120, thebellows 130, and the actuator 140 (refer to FIG. 3). The hexagonal testchamber 500 has a three dimensional hexagonal chamber shape (whereas thechamber 110 has a three dimensional rectangular shape). In the depictedembodiment, the hexagonal test chamber 500 is tilted as described abovein regard to the chamber 110. The hexagonal test chamber 500 can alsoinclude one or more of the other features described above in regard tothe chamber 110.

When cycling a liquid within a distal chamber with a free surfaceinterface between the liquid and a gas (e.g., a gas in the airspace182), the surface can become highly agitated. This can lead to gasbecoming entrained in the test liquid as bubbles. These bubbles mayreduce visibility of the valve and may come into contact with the valvewhich can potentially cause wear of the valve. It is thought that thesebubbles form when the motion of the liquid surface breaks the surfacetension. This can happen when the normal velocity of the liquid surfacebecomes significantly high, or if there is significant turbulent flow inthe liquid near the surface. The following three approaches (used aloneor in any combination of two or three of the approaches) reduce theissues discussed above in this paragraph: moving the liquid/gasinterface away from turbulent flow near the valve; increasing the areaof the liquid/gas interface; and using baffles in the zone of theliquid/gas interface.

Turning to FIG. 13, an example test chamber 600 includes a proximalchamber portion 610 that defines a proximal interior space, and a distalchamber portion 620 that defines a distal interior space. A valve holder630 is disposed between and adjacent to the proximal interior space andthe distal interior space. The valve holder 630 is configured to receivea valve 635 in a bore of the valve holder. An air or gas space 640 isincluded in the distal interior space of the distal chamber 620 when thechambers 610 and 620 contain a liquid. There is an interface 650 betweenthe liquid and a gas in the gas space. A shortest distance 660 between acenter of the valve 635 when in the bore and the interface 650 is atleast about 45 mm. In another example, a shortest distance 660 between acenter of the valve 635 when in the bore and the interface 650 is atleast about 50 mm. In yet another example, a shortest distance 660between a center of the valve 635 when in the bore and the interface 650is at least about 55 mm. In still another example, a shortest distance660 between a center of the valve 635 when in the bore and the interface650 is at least about 60 mm. In a further example, a shortest distance660 between a center of the valve 635 when in the bore and the interface650 is at least about 65 mm.

An area A_(s) of the interface 650 in cm² with the liquid at rest is setso that an agitated liquid depth D_(a) is no greater than a distance 670from the interface to a top edge of the valve 635. The agitated liquiddepth D_(a) is a distance that agitated liquid with bubbles reachesbelow the interface in cm during testing of a valve. The relationshipbetween A_(s) and D_(a) is substantially D_(a)=−mA_(s)+b (the equationfor a straight line) with m being in the range of about −0.6 to about−2.2 and b being in the range of about 13.1 to about 20.8. In a specificexample the relationship between A_(s) and D_(a) is substantiallyD_(a)=−1.6A_(s)+18.4. The test chamber 600 is configured to be useablewith the other relevant components of the system 100, such as theframework 120, the bellows 130, and the actuator 140 (refer to FIG. 3).The test chamber 500 can also include one or more of the other featuresdescribed above in regard to the chamber 110.

During testing, the liquid/gas surface/interface can become highlyagitated. One cause of this is surface waves which are reflected aroundthe test chamber. While these waves should not affect the net velocityof the surface (assuming the liquid is incompressible and the chamberwalls are rigid), it does increase the normal velocity of the surface inlocations. Placing walls (baffles) in the zone of the liquid/gasinterface reduces the ability of these waves to reflect, and alsominimizes sloshing.

Turning to FIG. 14, an example test chamber 700 includes a proximalchamber portion 710 that defines a proximal interior space, and a distalchamber portion 720 that defines a distal interior space. A valve holder730 is disposed between the proximal interior space and the distalinterior space. The valve holder 730 is configured to receive a valve ina bore of the valve holder. An air or gas space 740 is included in thedistal interior space when the chambers 710 and 720 contain a liquid745. There is an interface 750 between the liquid 745 and a gas in thegas space 740. At least one baffle 760 is located located in the distalinterior space at least partially on a first side of the interface andat least partially on a second side of the interface with the liquid 745at rest. The baffle reduces relection of waves in the liquid 745 offsides of the distal chamber portion 720.

FIG. 15 shows more detail of the baffle 760. In this example the baffleis in the form of a honeycomb with an array of through holes that ventthe liquid 745 and gas with each other. Of course the baffle 760 cantake other forms such as a curved or straight wall. A group of six tabs770 standoff a top surface of the baffle 760 by a small distance from atop substantially horizontal surface (or roof) 780 (see FIG. 14) of thedistal chamber portion.

While this specification contains many specific implementation details,these should not be construed as limitations on the scope of anyinvention or of what may be claimed, but rather as descriptions offeatures that may be specific to particular embodiments of particularinventions. Certain features that are described in this specification inthe context of separate embodiments can also be implemented incombination in a single embodiment. Conversely, various features thatare described in the context of a single embodiment can also beimplemented in multiple embodiments separately or in any suitablesubcombination. Moreover, although features may be described herein asacting in certain combinations and even initially claimed as such, oneor more features from a claimed combination can in some cases be excisedfrom the combination, and the claimed combination may be directed to asubcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. In certain circumstances, multitasking and parallel processingmay be advantageous. Moreover, the separation of various system modulesand components in the embodiments described herein should not beunderstood as requiring such separation in all embodiments, and itshould be understood that the described program components and systemscan generally be integrated together in a single product or packagedinto multiple products.

Particular embodiments of the subject matter have been described. Otherembodiments are within the scope of the following claims. For example,the actions recited in the claims can be performed in a different orderand still achieve desirable results. As one example, the processesdepicted in the accompanying figures do not necessarily require theparticular order shown, or sequential order, to achieve desirableresults. As an additional example, test parameters might be controlledby selecting any of the monitored parameters (e.g., actuatordisplacement 222, proximal pressure 244, distal pressure 242, pressuregradient 246, airspace 182, and others) as independent parameters andadjusting the remaining dependent parameters accordingly. In certainimplementations, multitasking and parallel processing may beadvantageous.

1-8. (canceled)
 9. A system for testing a valve, the system comprising:a chamber assembly comprising: a proximal chamber portion that defines aproximal interior space; a distal chamber portion that defines a distalinterior space, the distal interior space including a gas space, whereinwhen a liquid is inserted into the proximal and distal chambers there isan interface between the liquid and a gas in the gas space; and a valveholder that is disposed adjacent to the proximal interior space and thedistal interior space, the valve holder configured to receive the valvein a bore of the valve holder, wherein an area of the interface A_(s) incm² with the liquid at rest is set so that an agitated liquid depthD_(a) is no greater than a distance from the interface to a top edge ofthe valve, wherein the agitated liquid depth is a distance that agitatedliquid with bubbles reaches below the interface in cm during testing ofa valve.
 10. The system of claim 9, wherein a shortest distance betweena center of the valve when in the bore and the interface is at leastabout 50 mm.
 11. The system of claim 9, wherein a shortest distancebetween a center of the valve when in the bore and the interface is atleast about 55 mm.
 12. The system of claim 9, wherein a shortestdistance between a center of the valve when in the bore and theinterface is at least about 60 mm.
 13. The system of claim 9, wherein ashortest distance between a center of the valve when in the bore and theinterface is at least about 65 mm.
 14. The system of claim 9, furthercomprising one or more baffles which are located in the distal interiorspace at least partially on a first side of the interface and at leastpartially on a second side of the interface with the liquid at rest, theone or more baffles reducing reflection of waves in the liquid off sidesof the distal chamber portion.
 15. The system of claim 9, wherein therelationship between A_(s) and D_(a) is substantially D_(a)=−mA_(s)+bwith m being in the range of about −0.6 to about −2.2 and b being in therange of about 13.1 to about 20.8.
 16. The system of claim 15, whereinthe relationship between A_(s) and D_(a) is substantiallyD_(a)=−1.6A_(s)+18.4.
 17. A system for testing a valve, the systemcomprising: a chamber assembly comprising: a proximal chamber portionthat defines a proximal interior space; a distal chamber portion thatdefines a distal interior space, the distal interior space including agas space, wherein when a liquid is inserted into the proximal anddistal chambers there is an interface between the liquid and a gas inthe gas space; one or more baffles which are located in the distalinterior space at least partially on a first side of the interface andat least partially on a second side of the interface with the liquid atrest, the one or more baffles reducing reflection of waves in the liquidoff sides of the distal chamber portion; and a valve holder that isdisposed between the proximal interior space and the distal interiorspace, the valve holder configured to receive the valve in a bore of thevalve holder.
 18. The chamber assembly of claim 17, wherein a shortestdistance between a center of the valve when in the bore and theinterface is at least about 50 mm.
 19. The chamber assembly of claim 17,wherein a shortest distance between a center of the valve when in thebore and the interface is at least about 55 mm.
 20. The chamber assemblyof claim 17, wherein a shortest distance between a center of the valvewhen in the bore and the interface is at least about 60 mm.
 21. Thechamber assembly of claim 17, wherein a shortest distance between acenter of the valve when in the bore and the interface is at least about60 mm.